Category: Ethereum

Ethereum – Ganache Server Settings Click on the settings icon at the top right hand side of the screen as shown in the screenshot below − The server settings screen will appear as shown below − Here, you will be able to set the values of server address and the port number for your Ganache server. For the time being, leave these to their default values. The Network ID is an internal Blockchain identifier of Ganache server; leave this to its default value. The Automine button is in the ON state indicating that the transactions would be processed instantly. If you switched this off, it will ask you to enter the time in seconds after which the blocks would be mined. Account and Keys When you click on the Accounts & Keys menu option, you will see the following screen − Here you would be able to set the default balance for each account. The default value is 100. This now explains why you saw 100 ETH displayed for each account in the Desktop screenshot. You can also set the number of accounts on this screen. The value displayed in this screenshot is 2 and that is why the desktop showed only two accounts. Now, we will work out with the two settings’ screen; the knowledge of how these two work would suffice. Restart the server by clicking on the RESTART button in the right hand side of the screen. You will now return to the Desktop screen. Try inputting different values in the above two fields, restart the server and see its effect.

Ethereum – Interacting with Deployed Contract Now, you are ready to interact with the contract that you have deployed. Go back to MyEtherWallet desktop and click on the “Interact with Contract” tab as shown in the screenshot below − Paste the contract address that you previously copied in the “Contract Address” field. You also need to paste the “ABI / JSON Interface” of the contract on the above screen. To get the ABI, go to the Remix window and click on the ABI button as shown in the screenshot below. The ABI / JSON interface will be copied to the clipboard. Paste this in your favorite editor to examine the generated interface, which is shown below − ABI / JSON Interface [ { “constant”: false, “inputs”: [ { “name”: “newDeposit”, “type”: “uint256” } ], “name”: “send”, “outputs”: [], “payable”: false, “stateMutability”: “nonpayable”, “type”: “function” }, { “inputs”: [ { “name”: “initialAmount”, “type”: “uint256” }, { “name”: “initialValue”, “type”: “uint256” } ], “payable”: false, “stateMutability”: “nonpayable”, “type”: “constructor” }, { “constant”: true, “inputs”: [], “name”: “getAmount”, “outputs”: [ { “name”: “”, “type”: “uint256” } ], “payable”: false, “stateMutability”: “view”, “type”: “function” }, { “constant”: true, “inputs”: [], “name”: “getBalance”, “outputs”: [ { “name”: “”, “type”: “uint256” } ], “payable”: false, “stateMutability”: “view”, “type”: “function” } ] After you paste this JSON in the MyEtherWallet interface, you will notice that the ACCESS button below the JSON interface is now activated, as shown below − Click Access button to access the contract. Upon clicking the Access button, the contract address and function selection dropdown will appear on the screen like in the Remix editor. This is shown in the screenshot below − You may check the various functions of the contract as in the case of Remix deployment. Note that the contact is now deployed on an external Ganache Blockchain. Check the getAmount function; you will get the Amount value of zero and the getBalance will show a balance of 1000. Now try sending some money. It will present you a textedit control for entering the amount. When you write the contract, some “gas” would be used and you will be asked to confirm the transaction before writing it to the Blockchain. The transaction would be executed in a short while depending on the mining timing set by you on the Ganache server. After this, you can reexamine the value and the amount fields of the contract to verify that these are indeed modified. You may now examine the Ganache desktop to view the transactions that you have performed so far. A sample output is shown below − So far, you were both the contract creator and the contract executor. This does not make much sense, as you expect others to use your contract. For this, we will create another client for our Ganache Blockchain and send some money from the newly created account # 2 to the contract creator at account # 1.

Discuss Ethereum Looking at the advantages offered by Bitcoin − a digital currency, people wanted to use the concept of Blockchain in their own applications. People wanted to move out of their physical contracts to smart digital contracts where several issues like repudiation, transparency, security, etc. would be automatically addressed. The outcome of this effort resulted in the creation of Ethereum − a popular platform for creating distributed Blockchain applications that support smart contracts.

Ethereum – Summary You learned how to write your own digital contract in Solidity. You developed and tested the contract interface in the Remix IDE. For further multi-user testing, you deployed this contract on Ganache Blockchain. On Ganache, you created two user accounts. The first account was used for publishing the contract. The second account was used for consuming the contract. What is Next? The Ganache Blockchain that you used in this entire process is private and local to your machine. Once you are fully satisfied with the functioning of the contract, you may proceed to publish it on a real-life Ethereum Blockchain. However, doing so would require you to spend real money. In the demo application, we used 1000 ETH as default for each user account in Ganache. When you deploy your contract on a real-life Blockchain, you will have to buy the ETH by converting your own country’s currency to ETH. This currency would be stored in your wallet and you will be able to spend it the way you want.

Attaching Wallet to Ganache Blockchain You have now created a wallet; this wallet is a client interface to the Blockchain. We will attach the wallet to the Ganache Blockchain that you have started in the earlier lesson. To do so, click on the Network dropdown box as shown in the screenshot below − Go to the bottom of the list. You will see an option for “Add Custom Network / Node”. Select this item. Now, a screen will appear asking for the Ganache server address and the port to which it is listening. Type your Ganache server details – and Port: 8545. These would be the values set by you in the Ganache server setup. Give a name of your choice to this node. Click on the “Save & Use Custom Node” button. You will see the connected message at the bottom of the screen. At this point, your wallet is successfully connected to the Ganache Blockchain. You are now ready to deploy the contract on this connected Blockchain.

Ethereum – Useful Resources The following resources contain additional information on Ethereum. Please use them to get more in-depth knowledge on this. Useful Links on Ethereum − Official site of Ethereum. − Ethereum, its history and various other terms has been explained in simple language. Useful Books on Ethereum To enlist your site on this page, please drop an email to [email protected]

Ethereum – Quick Guide Ethereum – Introduction A huge success of Bitcoin raised interest in the minds of several to create their own currencies. Looking at the advantages offered by Bitcoin – a digital currency, people wanted to use the concept of Blockchain in their own applications. People wanted to move out of their physical contracts to smart digital contracts where several issues like repudiation, transparency, security, etc. would be automatically addressed. The outcome of this effort resulted in the creation of Ethereum – a popular platform for creating distributed Blockchain applications that support smart contracts. In this tutorial, you will learn how to create a distributed application (DAPP) on Ethereum platform. More specifically, you will learn how to write a contract, test it on a local Blockchain and finally deploy it on an external Blockchain for deep testing and commercial use. You will use Solidity, an object-oriented language for contract development. You will also use Remix, an open source IDE for developing and testing contracts. To deploy the tested contract on an external Blockchain, you will use Ganache. To interact with the contract you will need a client application. We will use MyEtherWallet to create a wallet for each such client. The contract creator will publish the contract. Any other client will look at the contact value by using the interface provided by the contract and send some money to the creator for executing a part of the contract. So let us begin by writing the contract. Ethereum – Smart Contracts There are several tools available to develop and test contracts. One of the simplest tools is provided on the official Ethereum site itself. The tool is called Remix, we will use this for our contract development. Remix for Contract Development Open the Remix IDE by typing in the following URL in your browser. The following screen will appear. In the center window, you will see some default code, which is a sample Solidity code. You will type your contract code in this code editor. Your code may be auto-compiled. Upon successful compilation of the code, you will be able to run the code in the same IDE. When you execute the contract methods, the results will be displayed in the same IDE window. There are facilities to debug the code and to unit test your project. These can be seen in the menu bar at the top right hand side as shown in the IDE screenshot below. You will be using these options shortly. You will now start writing your contract. Ethereum – Solidity for Contract Writing Solidity is an object-oriented language especially developed for contract writing. It is a high-level language, which inherits traits from C++, Python, and JavaScript. The Solidity compiler compiles your source code into bytecode that runs on Ethereum Virtual Machine (EVM). For quick understanding of the Solidity syntax, look at the sample code in the IDE. pragma solidity >=0.4.22 <0.6.0; contract Ballot { The first line is a directive to the compiler. The second line starts the definition of the contract. Within the contract, you declare variables such as − address chairperson; You can also define structures such as Proposal and create an array of these structure items. Examine this in the code window. You may then define a constructor which is invoked at the time of instantiating a contract. constructor(uint8 _numProposals) public { After the constructor, you will define several methods, which are the contract methods. In the sample contract, giveRightToVote is one such method having the following syntax − function giveRightToVote(address toVoter) public { The public keyword makes this method publicly invokable by any client who has access to the contract. Likewise, the sample contract defines three more methods called delegate, vote, and winningProposal. Examine these for your own understanding of the Solidity syntax. These are the prerequisites to writing your own contract. Explaining the full syntax of Solidity is beyond the scope of this tutorial. Ethereum – Developing MyContract We will name our contract MyContract as in the following declaration − contract MyContract { We will declare two variables as follows − uint amount; uint value; The variable amount will hold the accumulated money sent by the contract executors to the contract creator. The value field will hold the contract value. As the executors execute the contract, the value field will be modified to reflect the balanced contract value. In the contract constructor, we set the values of these two variables. constructor (uint initialAmount, uint initialValue) public { amount = 0; value = 1000; } As initially, the amount collected on the contract is zero, we set the amount field to 0. We set the contract value to some arbitrary number, in this case it is 1000. The contract creator decides this value. To examine the collected amount at any given point of time, we provide a public contract method called getAmount defined as follows − function getAmount() public view returns(uint) { return amount; } To get the balanced contract value at any given point of time, we define getBalance method as follows − function getBalance() public view returns(uint) { return value; } Finally, we write a contract method (Send). It enables the clients to send some money to the contract creator − function send(uint newDeposit) public { value = value – newDeposit; amount = amount + newDeposit; } The execution of the send method will modify both value and amount fields of the contract. The complete contract code is given below − contract MyContract { uint amount; uint value; constructor (uint initialAmount, uint initialValue) public { amount = 0; value = 1000; } function getBalance() public view returns(uint) { return value; } function getAmount() public view returns(uint) { return amount; } function send(uint newDeposit) public { value = value – newDeposit; amount = amount + newDeposit; } } Ethereum – Compiling the Contract Once you write the complete contract code, compiling it in this IDE is trivial. Simply click on the Autocompile checkbox in the IDE as shown

Ethereum – Creating Contract Users In this chapter, we will learn the creation of contract users on Ethereum. To create a user for our published contract, we will create another MyEtherWallet client attached to the same Ganache Blockchain that you have been using in the previous steps. Go to the MyEtherWallet screen and create a new wallet. Click on the contracts menu and select the “Interact with Contract” option as in the earlier case. Note that this new user is going to simply interact with the already published contract and not deploying his own contract. Specify the contract address and the ABI that you used in the earlier case. Now, click Access button and invoke send method. When asked, input some value say 100 ETH to be sent. Submit the transaction. Upon submission, the following screen will appear. To attach this new client to our Ganache Blockchain, go to Ganache Console. Click on the keys icon of account # 2 as shown in the following screenshot − You will get the private key for account # 2. Copy the key that you receive and use it in your newly created wallet as shown here − Click on the Unlock button to attach the wallet. When the wallet is successfully unlocked, write the desired send transaction. Generate the transaction by clicking on the “Generate Transaction” button. Make the transaction and wait for some time for it to reflect in the Blockchain. Now, execute “getAmount”, the amount shown should be 200 now. Execute “getBalance”. The value field should now be 800. Examine the transaction log to see the various transactions performed by different users.

Ethereum – Limitations of Remix The Remix IDE that you have used so far is good enough for development and initial testing of your contract. For real-life contracts, you need to test your functionality against various parameters. Remix cannot create real (non-test) user accounts to transfer funds between them. You have no control over the configuration of the Blockchain created by Remix. You cannot even monitor the execution of the transactions. Remix misses out on several advanced operations. Thus, we need to deploy our contract on a more sophisticated Blockchain that provides all these features. One such Blockchain is Ganache that you will learn about in our subsequent chapter.

Ethereum – Deploying the Contract In this chapter, we will learn how to deploy contract on Ethereum. Click on the Run menu option to deploy the contract. The following screen will appear. The contract name is shown in the highlighted list box. Below this, you will notice the Deploy button, click on it to deploy the contract. The contract will be deployed on the Remix built-in Blockchain. You will be able to see the deployed contract at the bottom of the screen. You can see this in the highlighted portion of the screenshot below. Notice, the presence of three method names in this highlighted region. Next, you will interact with the contract by executing the contract methods.